In the art of upward acting doors and flexible closure member or so called rollup type doors, a conventional construction comprises a door which is rolled onto and off of a rotatable drum to provide for moving the door between open and closed positions. In certain applications of rollup doors and, in particular, so called sheet doors, it may be desirable to mount the door and/or ship the door wherein the door rolled onto a drum would be disadvantageous. In low headroom door applications or applications wherein the enclosure or structure using the door is collapsible, a door which is adapted for rolling onto and off of a cylindrical drum would occupy too much space. Accordingly, there has been a need for a flexible type door, or so called sheet door, which may be stored in a generally planar or unrolled condition and moved between open and closed positions without requiring a storage drum or a continuous guide track between a vertical or closed position of the door and a horizontal or open position of the door, for example. It is to these ends that the present invention has been developed.